PHAGE TAXONOMY 435 



and phage are treated with uhraviolet hght (Weigle, 1953). 

 Similar results were described for the virulent phage T3 by 

 Weigle and Dulbecco (1953). Although various explanations 

 might be suggested for the origin of these mutants, the most in- 

 teresting is that they result from genetic recombination between 

 the phage genetic material and that of the host cell. 



5. Some rather different effects of combined ultraviolet irra- 

 diation of salmonella phage P22 and its host cells were inter- 

 preted in a similar manner by Garen and Zinder (1955). This 

 phage, like many others, is remarkably resistant to ultraviolet 

 light as compared with phage T2. Its resistance approaches 

 that of T2, however, if one measures the ability of both phages 

 to grow on bacteria that have been heavily irradiated themselves. 

 This could mean that radiation damage to phage P22, but not 

 to T2, can be eliminated by substitution of similar material 

 from the host, provided the latter is not irradiated. 



These and other observations, lately reviewed by Stent (1958), 

 are consistent with the hypothesis that part of the genetic ma- 

 terial of a phage is often homologous with part of the genetic ma- 

 terial of its host. If this hypothesis should prove correct, it 

 might suggest that a given phage is more closely related to its 

 host than to other phages attacking unrelated hosts. The in- 

 fluence that such hypotheses may have on the taxonomy of bac- 

 terial viruses and on the relation of bacteriophages to other vi- 

 ruses is obvious and need not be elaborated further. 



It seems clear that a Linnaean taxonomy for all viruses, or even 

 for the restricted group of bacterial viruses, is premature at the 

 present state of our information about these organisms. It would 

 seem wise under the circumstances to postpone the use of a bino- 

 mial nomenclature for these organisms at least until the taxonomic 

 relationships are somewhat clarified (see also Andrewes, 1957). 



7. Importance of Type Specimens 



In the earlier definition of a species it was customary to place a 

 type specimen in a museum or collection for use as a standard of 

 comparison by later taxonomists. In the new systematics the 



